There have been known many methods for producing porous silica-based particles, and the representative ones include a method in which porous particles are grown by the sol-gel process, and a method in which organic compounds or inorganic compounds are removed from composite particles to make the particles porous.
As for the method of producing porous particles by the sol-gel process, there has been proposed, for instance, a method in which alcohol, water and an acidic catalyst are added to tetraethyl orthosilicate to effect partial hydrolysis, then dibutyl phthalate is added to the mixture, and the mixture solution is further mixed with an ammonia aqueous solution containing a surfactant with agitation for its emulsification and the partial hydrolysate or the hydrolysate therein is polycondensed (Patent document 1), and a method in which tetraalkoxy silane or water glass (sodium silicate) is hydrolyzed in the presence of ammonia to generate a silica sol, then a carboxylic acid or carboxylate and an aliphatic nitrile compound are added to the sol to generate a silica gel (Patent document 2).
As for the method of producing porous particles by removing organic compounds from composite particles, there has been proposed, for instance, a method in which an activated silica and a cation-based surfactant are mixed and reacted in an alkaline phase to generate composite particles of the silica and the cation-based surfactant, then the composite particles are calcinated to remove the cation-based surfactant from the composite particles (Patent document 3), and a method in which water or acidic aqueous solution is added to a mixture of water-compatible organic solvent, alkylamine and silicate ester, or a mixture containing a combination of silicate ester and metal salt which is soluble in water-compatible organic solvent with agitation, then the generated silica-alkylamine composite products are grown to spherical particles and the alkylamine is removed from the composite particles (Patent document 4).
As for the method of producing porous particles by removing inorganic compounds from composite particles, there has been proposed, for instance, a method in which tetraalkoxysilane and boric compounds are hydrolyzed and polycondensed in a mixture solution of water and water-soluble organic solvent to generate spherical particles containing SiO2 and B2O3 as main components, then the B2O3 is eluted to remove the B2O3 from the composite particles (Patent document 5), and a method in which a silicate of alkali metal, ammonium or organic base, and an inorganic compound such as sodium aluminate are added simultaneously into an alkaline aqueous solution having pH 10 or more to generate colloidal particles consisting of the silica and the inorganic oxides, and then the inorganic oxides in the colloidal particles are removed with treatment by using an acid or a cation-exchange resin (Patent document 6).
On the other hand, the method has been already known in which at a boundary face of two-layer separated liquid including a layer of organic silicon compounds and a layer of water, or in the water layer, the organic silicon compounds are hydrolyzed and polycondensed to produce polyorganosiloxane particles and the like in the presence of organic solvent, alkali and/or surfactant (Patent document 7, Patent document 8 and Patent document 9). However, these methods are related to the method of producing dense silica-based particles having uniform particle diameters and the like, but are not related to the method of producing porous silica-based particles.
Patent document 1: Japanese Laid-open Patent Publication No. H08-91821
Patent document 2: Japanese Laid-open Patent Publication No. H08-26716
Patent document 3: Japanese Laid-open Patent Publication No. H08-34607
Patent document 4: Japanese Laid-open Patent Publication No. 2002-187712
Patent document 5: Japanese Laid-open Patent Publication No. H07-172814
Patent document 6: Japanese Laid-open Patent Publication No. H07-133105
Patent document 7: Japanese Laid-open Patent Publication No. H04-70335
Patent document 8: Japanese Laid-open Patent Publication No. 2000-17074
Patent document 9: Japanese Laid-open Patent Publication No. 2000-204168